1. Field of the Invention
Aspects of the present invention relate to a recording method, a recording apparatus, and an optical recording medium thereof that can improve the quality of a signal reproduced from a high multi-speed recording medium, and more particularly, to an information storage medium having an optimal recording waveform to improve a jitter effect caused by a fast recording process and a method and apparatus for recording data in the information storage medium.
2. Description of the Related Art
In general, information storage media, for example, optical discs, are widely used with optical pickup devices which record and/or reproduce information in a non-contact manner. Information storage media may be classified into compact discs (CDs) and digital versatile discs (DVDs) according to the information recording capacities of the information storage media. Examples of a recordable disc that can write, erase, and read information include a 650 MB CD-recordable (CD-R), a CD-rewritable (CD-RW), a 4.7 GB DVD+R/RW, a DVD-random access memory (RAM), and a DVD-R/RW. Examples of a read-only disc include a 650 MB CD-read only memory (ROM) and a 4.7 GB DVD-ROM. Furthermore, a high definition DVD (HD-DVD) having a recording capacity of over 20 GB is currently being developed.
When data is recorded in an optical disc, which is one type of an optical recording medium, marks are formed in tracks of the optical disc. For a read-only optical disc, such as a CD-ROM and a DVD-ROM, the marks are produced in the form of pits. For a recordable optical disc, such as a CD-R/RW and a DVD-R/RW/RAM, a phase change layer is coated with a phase change material that changes between an amorphous state and a crystalline state. The marks are formed in the recordable optical disc when the phase change layer undergoes a phase change. In order to optimize recording and/or reproducing features, the recordable optical disc employs write strategies. The write strategies are applied differently depending on the type of disc being written to. A writing condition may vary depending on disc drives used with the optical disc, which may result in incompatibility between an optical recording medium and a disc drive. In particular, an increased recording speed is needed to meet the demands of users who want to perform fast recording of information on optical discs having high storage capacity.
A high definition optical recording apparatus, such as a next generation blu-ray disc (BD) recorder, performs recording by using a run length limited (RLL)(1,7) code method in which a minimum value of a time period T of a clock pulse is equal to 2 T. When the (RLL)(1,7) code method is used, a laser output waveform for forming a recording mark with a predetermined length is composed of multi-pulses in which the number of write pulses generally increases according to the length of the recording mark. As shown in FIG. 1, if the length of the recording mark is equal to an integer multiple of N of the time period T, the laser output waveform uses a write strategy composed of N−1 write pulses.
When this method is used, it is difficult to switch a light source, i.e., a laser diode, in order to form multi-pulses at a high multi-speed. In addition, since recording is rapidly performed, there is no benefit to using multi-pulses. Moreover, when heat is rapidly emitted from the laser diode, sufficient heat is not easily transferred to an optical recording medium. Thus, the recording mark is not properly formed. In order to solve these problems, a write strategy using a new pulse is required.
FIGS. 1A and 1B illustrate a waveform diagram of a conventional recording waveform using a conventional multi-pulse write strategy. FIG. 1A illustrates a waveform diagram of a conventional recording waveform, and FIG. 1B illustrates a conventional multi-pulse write strategy. Referring to FIGS. 1A and 1B, a conventional recording waveform using a multi-pulse recording pattern is used to record non return to zero inverted (NRZI) data. Here, T denotes the cycle of a reference recording and/or reproducing clock signal. According to a method of recording a mark edge, a mark is recorded when the NRZI data is at a high level, and a space is formed when the NRZI data is at a low level. A recording waveform used to record the mark is referred to as a recording pattern. A recording waveform used to form the space (i.e. to erase the mark) is referred to as an erase pattern. In the conventional recording waveform, multi-pulses are used for forming the recording pattern, and a power level of each pulse is regulated to have one of three levels: Pw, Pe, and Pb. Specifically, the recording multi-pulses of the recording pattern used to form the marks have the power levels Pw and Pb, and the recording waveform used to form the space has the power level Pe. The power level Pe of the erase pattern for forming a space using low level NRZI data is maintained to be a predetermined direct current (DC) level. Here, Pw denotes a write power level, Pb denotes a bias power level, and Pe denotes an erase power level.
Referring to FIG. 1B, an N−1 write strategy is exemplified as a conventional multi-pulse recording strategy. A laser output waveform for forming a recording mark with a predetermined length is composed of multi-pulses in which the number of write pulses generally increases according to the length of the recording mark. If the length of the recording mark is an integer multiple of N of a time period T (e.g., 2 T 3 T etc), the laser output waveform has N−1 write pulses. For example, in order to record the recording mark of 5 T, the laser output waveform has four write pulses (5−1=4).
Table #1 below shows conditions for a recording method using a multi-pulse type write strategy.
Laser wavelength405 nmNumerical aperture0.85User data transfer rate35.965(Mbit/s) × 4 multi-speedRecording velocity4.92(m/s) × 4 multi-speedUser data capacity25 GbyteTrack pitch0.32 μm
Table #2 below shows a result obtained by comparing recording quality (also referred to as “jitter”) of recordings performed at various multi-speeds by using the conventional multi-pulse write strategy shown in FIG. 1.
Jitter at 1x multi-speed recording5.6%Jitter at 2x multi-speed recording6.4%Jitter at 4x multi-speed recording10.0%
Referring to Table #2 above, when recording is performed by using the conventional N−1 write strategy at 4× multi-speed (a rotation speed of about 10,000 RPM), jitter substantially increases in comparison with the case of jitter at 1× multi-speed recording or jitter at 2× multi-speed recording.
FIGS. 2A, 2B and 2C illustrate a simulation result of a recording mark formed in a blu-ray disc recordable (BD-R) during the process of 4× multi-speed recording using a conventional multi-pulse type write strategy. Specifically, FIG. 2A illustrates data for a recording mark of length 5 T; FIG. 2B illustrates a conventional multi-pulse write strategy; and FIG. 2C illustrates a simulation result of the recording mark using the conventional multi-pulse type write strategy shown in FIG. 2B. As shown by the irregular shape of the formed recording mark in the simulation result of FIG. 2C, heat transferred in response to a write pulse does not effectively form the recording mark at high speed. Since the simulation result of the recording mark shown in FIG. 2C has an irregular shape, it is not easy to optimally form the recording mark or to regulate the length of the recording mark by using the conventional multi-pulse type write strategy shown in FIG. 2B.
FIGS. 3A and 3B illustrate a waveform diagram of a conventional write strategy having a box type recording pattern using one pulse. FIG. 3A illustrates a waveform diagram of a conventional recording waveform, and FIG. 3B illustrates a conventional box type recording pattern. Referring to FIGS. 3A and 3B, a laser output waveform for forming a recording mark having a predetermined length is composed of only one pulse, irrespective of the length of the recording mark. A time period T is determined by the length of each pulse.
Table #3 below shows conditions for a recording method using the conventional box type write strategy shown in FIG. 3.
Laser wavelength405 nmNumerical aperture0.85User data transfer rate35.965(Mbit/s) × 4 multi-speedRecording velocity4.92(m/s) × 4 multi-speedUser data capacity25 GbyteTrack pitch0.32 μm
Table #4 below shows a result of recording quality (“jitter”) at 4× multi-speed recording by using the conventional box type write strategy.
Jitter at 4x multi-speed recording6.8%
FIGS. 4A, 4B and 4C illustrate a simulation result of a recording mark formed in a BD-R during the process of 4× multi-speed recording using the conventional box type write strategy shown in FIG. 3.
The conventional box type write strategy, which records at 4× multi-speed (a rotation speed of about 10,000 RPM), is used to solve the problems resulting from the conventional multi-pulse type write strategy. FIG. 4A illustrates data for a recording mark of length 5 T, FIG. 4B illustrates a conventional box type write strategy; and FIG. 4C illustrates a simulation result of the recording mark using the conventional box type write strategy shown in FIG. 4B. As FIG. 4C illustrates, the conventional box type write strategy decreases jitter in comparison with the conventional multi-pulse type write strategy.
As shown by the simulation result of FIG. 4C, the recording mark has a relatively uniform shape. This shows that sufficient heat is transferred so as to form the recording mark. However, unlike the simulation result shown in FIG. 2C, in the simulation result shown in FIG. 4C, a trailing portion of the recording mark is larger than a leading portion of the recording mark. This is because heat accumulation at the trailing portion of the recording mark increases relative to the heat accumulation accumulated at the trailing portion of the recording mark in the multi-pulse type write strategy. Thus, it is difficult to regulate the formation of a mark edge of the trailing portion of the recording mark.
In the above two methods, when recording is performed at a rotation speed equal to or greater than about 10,000 RPM, switching a laser diode to implement the conventional multi-pulse type write strategy as currently used is difficult. Furthermore, since the amount of heat transferred to a recording medium is small per unit time, using the conventional multi-pulse type write strategy for high speed recording is not appropriate for the formation of the recording mark. Therefore, the conventional box type write strategy may instead be used for recording so that more heat can be transferred per unit time with a pulse structure that is simpler to achieve in terms of switching the laser diode. As a result, the conventional box type write strategy decreases jitter compared to the jitter generated by the conventional multi-pulse type write strategy.
However, the simulation result shown in FIG. 4C illustrates that the trailing portion of the recording mark is larger than the leading portion of the recording mark. This change in the width of the recording mark occurs because of heat accumulation. Accordingly, an optimal write strategy is required for high multi-speed recording.